The invention relates to a conveying apparatus for tree trunks, and, in particular, to an apparatus for transporting tree trunks through a trunk measuring means. The apparatus comprises at least one transport chain which is movable in the transport direction and drivers which are secured at intervals to the transport chain and are driven by the latter. The drivers have engagement faces which are inclined in a direction transverse to the transport direction and are capable of sliding or rolling on a guide track.
Chain conveyors with pusher or driver chains are widely used in sawmill technology. The drivers, dogs or pushers consist generally of blocks which are connected to the chains or vertically disposed plate elements having a slightly V-shaped angled support or engaging face. The lowermost point of the driver is disposed in the center of the driver and the legs rise laterally in a direction .transverse to the conveying direction. The inclination angles of the driver legs are frequently between 10.degree. and 20.degree. to the horizontal. The engaging faces at the upper side of the drivers may be toothed to prevent trunks slipping on the drivers when starting up and accelerating the conveyor or under the action of any other forces acting on the conveyed trunks. The purpose of the V-shaped angled construction is to make the trunks assume as central a position as possible on the drivers under the action of gravity.
It is also known to optically measure tree trunks for an optimum cutting division. This measuring can take place in the region of a chain bed conveyor, with both an intermittent or a continuous advance of the trunks on the conveyor.
Generally, the opitcal measurement of trunks has been restricted to measuring the diameter of the trunk at predetermined intervals in order to determine the cutting possibilities and thus the utilizability of the trunk cross-section over the length of the trunk. If with a raster camera or a photo-cell means both outer trunk side borders are simultaneously detected at a point to determine the trunk diameter from their position difference, it is of no consequence whether the trunk on its advance up to the next measuring position changes its position on the chain conveyor because of certain support instabilities. The measurement result is not influenced by the three-dimensional position the measuring point has on the trunk.
Since tree trunks are only very rarely ideally straight, however, further steps in optical measuring have recently been taken where, apart from the trunk diameter, attempts are made at various points to detect the position of the trunk axis in order to determine the curvature variation thereof in the manner of a locus curve. From the data acquired and evaluated with the aid of a computer on the basis of the trunk curvature, the optimum severing cut positions are determined to obtain individual portions which are as straight as possible for an optimum cross-section utilization.
In measuring methods in which the path of the trunk axis is measured, it is important that the trunk in the necessary intermittent or continuous advance movement through the measuring station retains the three-dimensional position it has assumed. This requires stable support of the trunk on the chain conveyor. In particular, relatively large trunks having branch stubs can assume a position on the previously described integrally angle-shaped drivers in which although they rest relatively centrally on the drivers they are located on branch stubs. When this occurs the trunks are in an unstable support position in which they can easily rock to and fro between two locations due to the movement forces of the conveyor.